Sulfasalazine

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Sulfasalazine, a sulfonamide, generally is considered a prodrug since the diazo bond is cleaved in vivo to provide sulfapyridine and 5-aminosalicyclic acid (mesalamine); the drug exhibits antibacterial and anti-inflammatory activity.

Uses

Sulfasalazine is used in the management of mild to moderate ulcerative colitis in adults and children 2 years of age or older and also is used in the management of Crohn's disease in adult and pediatric patients. In addition, sulfasalazine administered as delayed-release tablets is used for the management of rheumatoid arthritis in adults and for the management of polyarticular course juvenile rheumatoid arthritis in children 6-16 years of age.

Ulcerative Colitis

Sulfasalazine is used in the treatment of mild to moderate ulcerative colitis in conjunction with the usual supportive and dietary measures. Corticosteroids are more effective than sulfasalazine in treating acute attacks and concomitant administration of corticosteroid retention enemas may be required. Patients who do not respond to concomitant sulfasalazine and topical corticosteroid therapy or who have extensive intestinal involvement may require systemic corticosteroids. Sulfasalazine is more effective than corticosteroids in reducing the frequency and severity of relapses, and is usually used for maintenance therapy. The manufacturers state that sulfasalazine may also be used as an adjunct in the treatment of severe ulcerative colitis. Controlled studies supporting this indication are lacking, and other treatment such as parenteral corticosteroids or surgery is generally required.

Crohn's Disease

Sulfasalazine is used in the treatment of active Crohn's disease, but its role in the management of this condition is not as well defined as in the treatment of ulcerative colitis. Sulfasalazine may be used as initial drug therapy in patients with mild to moderately active disease, especially in those with ileocolonic or colonic involvement. However, sulfasalazine may not be effective in patients with small bowel disease. There is some evidence that concomitant therapy with sulfasalazine and corticosteroids may not be more effective than either drug alone, but some subgroups of patients may have a better response to combined therapy (e.g., those with disease localized in the colon). Sulfasalazine does not appear to be useful for maintenance therapy in Crohn's disease once a remission has been attained or following surgical resection.

Rheumatoid Arthritis in Adults

Sulfasalazine is used in the treatment of rheumatoid arthritis in adults whose symptoms progress despite an adequate regimen of nonsteroidal anti-inflammatory agents (NSAIAs). Sulfasalazine is one of several disease-modifying antirheumatic drugs (DMARDs) that can be used when DMARD therapy is appropriate. (For further information on the treatment of rheumatoid arthritis, see Uses: Rheumatoid Arthritis, in Methotrexate 10:00.) Analgesic and/or NSAIA therapy in conjunction with sulfasalazine usually is recommended in patients with rheumatoid arthritis, at least until the beneficial effects of sulfasalazine are apparent. Administration of sulfasalazine alone is not a complete treatment for rheumatoid arthritis, and the drug only should be used as one part of a comprehensive treatment program, including non-drug therapies such as rest and physical therapy. Unlike anti-inflammatory agents, sulfasalazine does not produce immediate response in patients with this condition. Sulfasalazine has been used in combination with other DMARDs (e.g., azathioprine, gold compounds, hydroxychloroquine, methotrexate, penicillamine) and/or systemic corticosteroids. In patients with rheumatoid arthritis, sulfasalazine improves grip strength, decreases erythrocyte sedimentation rate, reduces joint tenderness, and decreases duration of early morning stiffness. Limited data indicate that sulfasalazine appears to be as effective as gold compounds, hydroxychloroquine, or penicillamine in the management of rheumatoid arthritis.

Juvenile Arthritis

Sulfasalazine is used for the management of the signs and symptoms of polyarticular course juvenile rheumatoid arthritis in children who have not responded adequately to NSAIAs. Safety and efficacy of sulfasalazine for the management of polyarticular course juvenile rheumatoid arthritis in children 6-16 years of age is supported by evidence from adequate and well-controlled studies in adults. Extrapolation of data from adults with rheumatoid arthritis to children with polyarticular course juvenile rheumatoid arthritis is based on similarities in disease and response to therapy in these patient populations and published studies. Because of the high frequency of adverse effects in children receiving sulfasalazine for the management of systemic course juvenile rheumatoid arthritis, use of the drug in children with this type of arthritis is not recommended.

Other Uses

Sulfasalazine has been used with some success in the treatment of granulomatous colitis and scleroderma, and was reportedly beneficial in the treatment of collagenous colitis in one patient.

Drug Interactions

Sulfasalazine shares the potential drug interactions of the sulfonamides. In addition, sulfasalazine may interact with other agents. It has been postulated that concomitant administration of antibiotics may alter the action of sulfasalazine by altering intestinal flora and consequently sulfasalazine metabolism. Sulfasalazine chelates iron, altering distribution of sulfasalazine in the intestinal lumen, interfering with its absorption and resulting in lower blood concentrations of sulfasalazine. Sulfasalazine inhibits folic acid absorption, interferes with folic acid metabolism, and may result in decreased serum folic acid concentrations and possibly folic acid deficiency in some patients. Several mechanisms appear to be involved, including inhibition of hepatic folate metabolism, intestinal transport of folic acid, and jejunal brush-border folate conjugase. Some clinicians suggest that folic acid deficiency may be prevented in patients receiving sulfasalazine by increased dietary intake of folic acid, taking the drug between meals, and/or by administration of folic acid supplements.

Mechanism of Action

Although the precise mechanism of action of sulfasalazine in the treatment of ulcerative colitis has not been determined, one possible mechanism is that sulfasalazine serves as a vehicle to deliver sulfapyridine and 5-aminosalicylic acid (mesalamine) to the colon in higher concentrations than can be achieved by oral administration of these metabolites alone. Once these agents have reached the colon, therapeutic effect may result from antibacterial action of sulfapyridine or topical anti-inflammatory action of 5-aminosalicylic acid. Other actions which may explain the activity of sulfasalazine include changes in organizational patterns in intestinal flora, reduction in Clostridium and Escherichia coli in the stools, inhibition of the synthesis of prostaglandins known to elicit diarrhea and affect mucosal transport, alteration in the secretion and absorption of fluids and electrolytes by the colon, and/or immunosuppression. Although it has been proposed that the therapeutic effects may also be related to the affinity of the drug for connective tissue and serosal membranes, ulcerative colitis primarily affects the mucosa which has very little connective tissue.

Pharmacokinetics

Absorption

About 10-15% of a dose of sulfasalazine is absorbed as unchanged drug from the small intestine. Part of the absorbed sulfasalazine is apparently excreted via the bile into the intestine. The remainder of an oral dose of sulfasalazine passes intact into the colon where the azo-linkage is cleaved by intestinal flora to form sulfapyridine and 5-aminosalicylic acid (mesalamine). Sulfapyridine is rapidly absorbed from the colon. Only a small portion of the 5-aminosalicylic acid present in the colon is absorbed. Following administration of a single 2-g oral dose of sulfasalazine to healthy adults, peak serum sulfasalazine concentrations occur within 1.5-6 hours and average 14 mcg/mL. Peak serum sulfapyridine concentrations occur within 6-24 hours and average 21 mcg/mL. Following administration of a single 2-g oral dose of enteric-coated sulfasalazine, peak serum sulfasalazine concentrations occur within 3-12 hours and average 6 mcg/mL, and peak sulfapyridine concentrations occur within 12-24 hours and average 13 mcg/mL. The mean serum concentration of total sulfapyridine (sulfapyridine and its metabolites) tends to be greater in patients who are slow acetylator phenotypes than in fast acetylator phenotypes. In one study of colitis patients receiving sulfasalazine in doses ranging from 3-6 g daily, mean steady-state serum concentrations in fast acetylators were 17.6 mcg of sulfasalazine per mL, 31 mcg of total sulfapyridine per mL, and 1 mcg of 5-aminosalicylic acid per mL. In slow acetylators, mean steady-state serum concentrations were 18. mcg of sulfasalazine per mL, 53.7 mcg of total sulfapyridine per mL, and 1 mcg of 5-aminosalicylic acid per mL. Serum concentrations of total sulfapyridine in excess of 50 mcg/mL appear to correlate with adverse effects, while concentrations of 20-50 mcg of total sulfapyridine per mL appear to correlate with clinical improvement. Serum concentrations of 5-aminosalicylic acid range from 0-4 mcg/mL in patients with ulcerative colitis receiving sulfasalazine.

Distribution

In animals, relatively high concentrations of sulfasalazine are present in serous fluid, liver, and the intestinal wall. Sulfapyridine is distributed to most body tissues. Only very small amounts of unchanged sulfasalazine are distributed into milk, but sulfapyridine concentrations in milk are about 30-60% of those in serum. Unchanged sulfasalazine, sulfapyridine and its metabolites, and 5-aminosalicylic acid and its acetylated metabolite cross the placenta.

Elimination

In one study in healthy individuals receiving 4-g doses of sulfasalazine, the mean serum half-life of sulfasalazine was reported to be 5.7 hours following a single dose and 7.6 hours following multiple doses.

The half-life of sulfapyridine was reported to be 8.4 hours following a single dose, and 10.4 hours following multiple doses of sulfasalazine. Sulfasalazine is cleaved by intestinal flora in the colon to form sulfapyridine and 5-aminosalicylic acid.Following absorption, sulfapyridine undergoes hepatic N 4-acetylation and ring hydroxylation followed by conjugation with glucuronic acid. A small portion of 5-aminosalicylic acid is absorbed and undergoes N 4-acetylation; the major portion is excreted in the feces. Most of a dose of sulfasalazine is excreted in the urine. Generally, unchanged sulfasalazine accounts for up to 15%, sulfapyridine and its metabolites account for about 60%, and 5-aminosalicylic acid and its metabolites account for 20-33% of a dose. One study has shown urinary excretion of total sulfapyridine to be higher in patients in remission as compared to unimproved patients. Although total fecal excretion of sulfasalazine and its metabolites depends on GI transit time and the activity of the intestinal bacteria, one study has shown fecal excretion to account for about 5% of a daily dose (primarily as sulfapyridine metabolites).

Chemistry and Stability

Chemistry

Sulfasalazine is synthesized by diazotization of sulfapyridine and coupling of the diazonium salt with salicylic acid. Sulfasalazine is generally considered a prodrug since the diazo bond is cleaved in vivo to provide sulfapyridine and 5-aminosalicylic acid (mesalamine). Sulfasalazine occurs as a bright yellow or brownish-yellow, odorless, fine powder and has solubilities of less than 0.1 mg/mL in water and approximately 0.34 mg/mL in alcohol at 25°C.

Stability

Commercially available sulfasalazine conventional tablets and sulfasalazine delayed-release tablets should be stored at a controlled room temperature of 25°C, but may be exposed to temperatures ranging from 15-30°C.